Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals (e.g. cellphones, tablet computers and other electronic devices). Each wireless terminal communicates with one or more base stations via transmissions on one or more uplinks and downlinks. A downlink (or forward link) refers to the communication link from the base stations to the wireless terminal, and an uplink (or reverse link) refers to the communication link from the wireless terminal to the base station. These communication links may be established via a single-in-single-out (SISO), multiple-in-single-out (MISO), or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple transmit antennas and multiple receive antennas for data transmission. A MIMO channel formed by the transmit and receive antennas may be decomposed into independent channels, which are also referred to as spatial channels. Each of the independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensions created by the multiple transmit and receive antennas are utilized.
A MIMO system supports time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the uplink and downlink transmissions are within the same frequency region so that the reciprocity principle allows the estimation of the downlink channel from the uplink channel. This enables the base station to extract transmit beamforming gain on the downlink when multiple antennas are available at the base station.
The primary purpose of the base station is to provide connectivity between a wireless terminal or terminals and the core communications network. In a UMTS radio access network (RAN), the functionalities of a base station may be split across two network elements: the Radio Network Controller (RNC) handles, among other functions, connection setup, resource assignment and mobility; the base node (NodeB) configured to handle the radio transmission and reception to and from wireless terminals as well as the resource allocation for connected users on the shared channels.
To establish a call connection between a wireless terminal and a base station, a Radio Access Bearer (RAB) is needed. The RAB carries voice or other data between the wireless terminal and the core communication network. There are different types of RABs for different types of data, such as, for example, voice data, streaming data (e.g. streaming a video clip), interactive data (e.g. interacting with a website) and others. Simultaneous voice and data connections require multiple RABs and may be referred to as Multi-RAB or MRAB connections. In the early days of combined voice and data networks, e.g. 3G UMTS, simultaneous voice and data connections were not prevalent. However, newer wireless terminal devices (e.g. touch-screen cellular telephones) increasingly use voice and data connections simultaneously. MRAB calls are known to experience an increased rate of dropped calls or connections compared to single RAB calls or connections. One cause for may be due to, for example, variable wireless signal conditions. Accordingly, there is a need to improve the communication between a wireless terminal and a base station during MRAB calls.